1. Field of the Invention
The present invention relates to a metal mask; particularly, the present invention relates to a metal mask having an anti-tension design.
2. Description of the Prior Art
Because the organic light emitting diode display (OLED) has characteristics such as low power consumption, thin thickness, and self-light-emitting, people have paid more attention to the OLED recently. In a manufacturing process of the OLED, the quality of a vapor deposition process will directly affect a yield rate of the OLED, wherein a metal mask is one of the most important units under the vapor deposition process. FIG. 1 is a top view of a traditional metal mask. As shown in FIG. 1, the traditional metal mask 10 is a long thin slice having several mask bodies 12 disposed along the extending direction of the metal mask 10. In the vapor deposition process, each mask body 12 corresponds to a substrate. The mask body 12 is a structure having many tiny holes that allow liquid crystal molecules to pass therethrough under the vapor deposition process to form a coating film and liquid crystal molecules can be arranged in a predetermined shape. As such, the smoothness of a surface of the traditional metal mask 10 and a horizontal position of the traditional metal mask 10 disposed during the vapor deposition process are closely related to the yield rate of the organic light emitting diode display.
As shown in FIG. 1, in order to smoothen and keep the surface of the traditional metal mask at the horizontal position before the vapor deposition process, tension force is applied by a clamp device at two ends of the traditional metal mask 10 (shown by the arrows). A compressed stress occurred in a width direction of the thin slice traditional metal mask 10 under the tension force. However, when the tension force is beyond a critical value, wrinkles will appear on the surface of the traditional metal mask 10 because of the excessive stress along the width direction. Once wrinkles appear on the surface of the metal mask, the path of the mask body 12 along which liquid crystal molecules pass through will be affected, resulting in a poor vapor deposition quality because of change in smoothness. In order to prevent the change in smoothness mentioned above, the structure of the traditional metal mask requires improvement.